The night before He died for her, Christ was thinking of His bride. When He knelt to wash His disciples’ feet, He was the Bridegroom washing His bride to make her radiant. In the strength of humility, He ministered to the needs of His bride. In the posture of a slave, He led her into greater devotion to Himself. 
Having been on His knees, He would now propose. Although it would become the night of His betrayal, it was first the night of His betrothal. During the Passover meal, He used both the gesture and the words of the traditional Jewish betrothal: drinking from a cup of wine and then handing it to His followers, He said, “This is my blood of the covenant.”
While this phrase would have been familiar to the disciples, hearing Jesus speak those words to them would have been startling—as surprising as it had been to see Him washing their feet. He was proposing an unconditional, blood covenant to them—not unlike a marriage. When they then drank from the cup that Christ held out to them, the disciples were accepting His offer of devoted relationship and were pledging themselves to Him as covenant partners.
Each time that we “drink this cup,” we are not only remembering His sacrifice for us; we are also renewing our vows to Him.
 Ephesians 5:25-30